Wimax standards and Security The Wimax

Synchronization to Target BS Downlink

To connect with the target BS, the MS synchronizes with the downlink transmissions of the target BS and obtains downlink (DL) and uplink (UL)

transmission parameters. If the MS had previously received an MOB_NBR- ADV message including target BSID, physical frequency, DCD, and UCD, this synchronization process can be shortened. Otherwise, the MS synchronizes with the target BS by scanning the possible channels of DL frequency band until it finds a valid DL signal.

5. Use of Scanning and Association Results

An MS scans the target neighboring BSs and has the option to try association. If the target BS has previously received HO notification over the backbone from the serving BS, the target BS can place a fast ranging information ele- ment (Fast_Ranging_IE) in the UL-MAP to allocate a noncontention-based initial ranging opportunity. Therefore, the MS can use the noncontention- based initial ranging opportunity by scanning the UL-MAP of the target BS for fast HO ranging process.

6. Ranging

An MS and a target BS conduct an initial ranging or HO ranging after the synchronization with the target BS downlink. An MOB_BSHO-REQ or MOB_BSHO-RSP message informs the MS of the common time inter- val at which the dedicated initial ranging transmission opportunity for the MS will be provided by the target BS. Therefore, the MS can receive the Fast_Ranging_IE in the UL-MAP of its target BS, which includes a noncontention-based initial ranging opportunity. If the MS confirms that ini- tial ranging opportunity, it can transmit an RNG-REQ code to the target BS without access collision. This operation enables fast ranging because the target BS provides a dedicated UL resource for the ranging request.

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